Could you kill someone using Enchantment School Wizard's Hypnotic Gaze forever?

Question

If your character really hated someone very much and had enough resources to stay alive longer than the hypnotized target (Let's say, through the Constructed Resilience feature or something similar), could you just stay by the target's side for days until he starved to death?

As described in the Hypnotic Gaze feature:

[...]The charmed creature's speed drops to 0, and the creature is incapacitated and visibly dazed.

On subsequent turns, you can use your action to maintain this effect, extending its duration until the end of your next turn. However, the effect ends if you move more than 5 feet away from the creature, if the creature can neither see nor hear you, or if the creature takes damage.[...]

Then that's it? Is it just necessary for the target to fail the test and then wait alongside the target until the end of time?

Answer 1

This appears to be a slow but effective (and exhausting) assassination technique

If you are a warforged or some other race that doesn't need to eat or drink, then you could indeed use your action every turn to maintain your Hypnotic Gaze for however many days it takes for the target to suffer 6 levels of exhaustion and die. Note that if you attempt this, you cannot take any rests during this process, so the DM may bring in the optional rule from XGtE for going without a long rest, wherein you must succeed on a Constutution saving throw every 24 hours (with the DC rising by 5 each day) or suffer a level of exhaustion. Of course, your target would also be subjected to the same saving throws in addition to those for going without water and food, so as long as you have a good modifier for the saving throw, this might work in your favor.

Of course, all of this assumes you can get the (presumably hostile) target alone with you and get close enough to use the ability, and that no one will come looking for them and interrupt you, etc. This is probably the most difficult part of making such a plan work. If your enemy is worth assassinating in this way, they probably have allies who won't leave you alone for several days to get this done.

Answer 2

Unlikely, as it only works if neither of you falls asleep

The PH states on p. 186 under Resting:

Heroic though they might be, adventurers can’t spend every hour of the day in the thick of exploration, social interaction, and combat. They need rest—time to sleep and eat

So it's pretty clear that the default assumption is that creatures need rest and cannot just keep up without ad infinitum. It still might be possible with a conscious effort to do so — the real-world record for going without sleep is 11 days. For this there are some rules, too. The PH lists this under constitution checks:

The DM might call for a Constitution check when you try to accomplish tasks like the following: […]

• Go without sleep

Under the core rules¹ you only can keep this up if your DM does not impose such checks upon you, or if you succeed on them. But more importantly, it works only if they rule that the victim who cannot take actions does not fall asleep either.

The DM calls for an ability check when a character or monster attempts an action (other than an attack) that has a chance of failure. When the outcome is uncertain, the dice determine the results.

It is up to the victim to decide if they want to fight their need to sleep. If they do not, they would just fall asleep. (Even if they want to stay awake, they might auto-fail, depending on how the DM rules²).

Mechanically, the Incapacitated condition only restricts your ability to take actions. It doesn't say that it blocks you from thinking or taking decisions. Dazed is not a defined condition (in fact, this is the only time the term is used in the PH). Its dictionary definition is (Oxford Languages):

unable to think or react properly

While this may impair your thinking and decision making, for example for formulating complex plans, this is not a condition that would stop you from naturally falling asleep either.

So, it seems unlikely this will work, not primarily because you have to stay awake, but because you have no way to force your victim to stay awake.

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¹ There are also optional rules in Xanathar's that, as explained in this answer use saving throws instead of ability checks, and might work more in your favor.

² It's not clear if the check to remain awake actually would require an action, not all of them do. If the DM decided it would, the victim cannot succeed, even if it decides to fight the natural need to sleep, because it cannot take the action, and it will fall asleep. (See also Is it possible to fail an ability check on purpose? for more on failing ability checks).